The synergistic effect of steam explosion pretreatment and sodium hydroxide post-treatment of Lespedeza stalks (Lespedeza crytobotrya) has been investigated in this study. In this case, Lespedeza stalks were firstly exploded at a fixed steam pressure (22.5 kg/m(2)) for 2-10 min. Then the steam-exploded Lespedeza stalks was extracted with 1 M NaOH at 50 degrees C for 3 h with a shrub to water ratio of 1:20 (g/ml), which yielded 57.3%, 53.1%, 55.4%, 52.8%, 53.2%, and 56.4% (% dry weight) cellulose rich fractions, comparing to 68.0% from non-steam-exploded material. The content of glucose in cellulose rich residues increased with increment of the steaming time and reached to 94.10% at the most severity. The similar increasing trend occurred during the dissolution of hemicelluloses. It is evident that at shorter steam explosion time, autohydrolysis mainly occurred on the hemicelluloses and the amorphous area of cellulose. The crystalline region of cellulose was depolymerized under a prolonged incubation time. The characteristics of the cellulose rich fractions in terms of FT-IR and CP/MAS (13)C NMR spectroscopy and thermal analysis were discussed, and the surface structure was also investigated by SEM.
"Soluble nitrogen content in SERS increased with the higher pretreatment pressure, because the interaction between soluble nitrogen and SERS was mainly physical absorption. Higher pressure could lead to larger specific surface area that was more suitable for physical absorption (Wang et al., 2009). The soluble nitrogen appeared to more easily diffuse out of the biomass by washing, which could be used as inorganic nitrogen resource. "
[Show abstract][Hide abstract] ABSTRACT: Improving nitrogen content and enhancing enzymatic hydrolysis are key processes involved in cellulosic ethanol production. Steam explosion (SE) associated with NH4Cl preimpregnation was carried out to investigate effects of the pretreatment on nitrogen content, enzymatic digestibility, and ethanol production. Results showed that nitrogen content in pretreated samples increased, which can be used as nitrogen resource for ethanol fermentation. The highest glucose yield of sample pretreated by 1.4MPa SE with 90g/l NH4Cl preimpregnation was 62.64%, which was 2.1 and 0.2 times higher than that of untreated sample and 1.4MPa SE pretreated sample, respectively. Ethanol yield of sample pretreated by 1.1MPa SE with 135g/l NH4Cl preimpregnation resulted in 1.93 and 0.69 times higher than that of untreated sample and 1.1MPa SE pretreated sample, respectively. This novel pretreatment improved nitrogen content and enhanced enzymatic digestibility under mild conditions, and could be recommended to further industrial application.
"The composition of structural carbohydrates was determined using National Renewable Energy Laboratory (NREL) protocol (Sluiter et al., 2007), and analyzed by the high-performance anion exchange chromatography (HPAEC) (Dionex, ISC 3000, US) system as reported in the previous literature (Wang et al., 2009). The molecular weight distribution of the cellulose-rich samples was determined by gel permeation chromatography (GPC) after the tricarbanilation derivatization (Josefsson et al., 2001). "
[Show abstract][Hide abstract] ABSTRACT: In order to establish the correlation between hemicelluloses removal and bioconversion efficiency of cellulose, fractionation process with increasing NaOH concentration selectively released the hemicellulosic polymers with increasing molecular weight and decreasing degree of substitution. Not only the initial hydrolysis rates also the concentrations of glucose and ethanol were significantly enhanced from 5.93 and 8.39g/L to the range of 8.67-9.60g/L and 11.53-13.71g/L after alkaline treatment, respectively. However, the maximum conversions of cellulose to glucose (61.9%) and ethanol (64.6%) were achieved as 33.0% hemicelluloses was still remained. Excluding the negligible effect on the crystal transformation of cellulose, the improvement of bioconversion efficiency was resulted from the synergetical effects of surface exposure, multi-layers collapse and the hydrophilic property of the cellulosic substrate. It is critical task to balance these factors by the partial removal of hemicellulosic component, not complete.
"Therefore, a pretreatment to separate the lignin from the substrate is a promising approach to increase the enzymatic digestibility of cellulose. Different pretreatment methods including chemical (acid, alkali, ozone, alkaline peroxide), physical (comminution, hydrothermolysis ), and physicochemical (steam explosion, ammonia fiber explosion ) techniques have been developed for lignocellulosic waste pretreatment (Karagöz et al., 2012; García-Cubero et al., 2009; Wang et al., 2009; Antoni et al., 2007; Asada et al., 2011). Among the pretreatment methods, steam explosion, dilute acid, alkaline, and oxidative pretreatment methods have been widely employed for improving enzymatic hydrolysis. "
[Show abstract][Hide abstract] ABSTRACT: A potential commercial pretreatment for furfural residues (FRs) was investigated by using a combination of green liquor and hydrogen peroxide (GL-H2O2). The results showed that 56.2% of lignin removal was achieved when the sample was treated with 0.6g H2O2/g-DS (dry substrate) and 6mL GL/g-DS at 80°C for 3h. After 96h hydrolysis with 18FPU/g-cellulose for cellulase, 27CBU/g-cellulose for β-glucosidase, the glucose yield increased from 71.2% to 83.6%. Ethylenediaminetetraacetic acid was used to reduce the degradation of H2O2, the glucose yield increased to 90.4% after the addition of 1% (w/w). The untreated FRs could bind more easily to cellulase than pretreated FRs could. The structural changes on the surface of sample were characterized by X-ray photoelectron spectroscopy. The results indicated that the surface lignin could be effectively removed during pretreatment, thereby decreasing the enzyme-lignin binding activity. Moreover, the carbonyl from lignin plays an important role in cellulase binding.
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